FIELD OF THE INVENTION
This invention relates to a process for manufacturing high purity silica. Particularly, it relates to a process for manufacturing high purity silica having a very low content of impurities such as alkali metals, chlorine and radioactive impurities such as uranium from an aqueous alkali silicate solution.
High purity silica is used as a filler, dispersant and the like and as a material for transparent vitreous silica, special ceramics and the like, and is expected to be used as a material for filler for resin compositions for encapsulating electronic parts.
As materials for encapsulating electronic parts, there are used synthetic resin compositions containing an inorganic filler such as silica. It is considered to be advantageous to incorporate inorganic fillers as much as the moldability permits from the viewpoint of physical properties such as expansion coefficient, thermal conductivity, moisture permeability and mechanical properties and cost, and silica type fillers are considered to be most preferable. However, with an enhancement of the degree of integration of elements of electronic parts, there is caused a problem of erroneous working of elements, which seems to be attributable to .alpha.-rays emitted from slight amounts of radioactive elements such as uranium, thorium and the like contained in encapsulating materials used, particularly silica type fillers, in an amount of tens to hundreds ppb. It is desired to further reduce the content of such impurities in silica.
The process of this invention aims at meeting this desire.